From: Michael Paquier <michael@paquier.xyz>
Date: Mon, 11 May 2026 12:13:46 +0000 (-0700)
Subject: Apply timingsafe_bcmp() in authentication paths
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5924e256c499c010dd369984498c8d5a4ee17894;p=thirdparty%2Fpostgresql.git

Apply timingsafe_bcmp() in authentication paths

This commit applies timingsafe_bcmp() to authentication paths that
handle attributes or data previously compared with memcpy() or strcmp(),
which are sensitive to timing attacks.

The following data is concerned by this change, some being in the
backend and some in the frontend:
- For a SCRAM or MD5 password, the computed key or the MD5 hash compared
with a password during a plain authentication.
- For a SCRAM exchange, the stored key, the client's final nonce and the
server nonce.
- RADIUS (up to v18), the encrypted password.
- For MD5 authentication, the MD5(MD5()) hash.

Reported-by: Joe Conway <mail@joeconway.com>
Security: CVE-2026-6478
Author: Michael Paquier <michael@paquier.xyz>
Reviewed-by: John Naylor <johncnaylorls@gmail.com>
Backpatch-through: 14
---

diff --git a/src/backend/libpq/auth-scram.c b/src/backend/libpq/auth-scram.c
index 0267edb29cd..4bac15fc5c1 100644
--- a/src/backend/libpq/auth-scram.c
+++ b/src/backend/libpq/auth-scram.c
@@ -579,7 +579,7 @@ scram_verify_plain_password(const char *username, const char *password,
 	 * Compare the secret's Server Key with the one computed from the
 	 * user-supplied password.
 	 */
-	return memcmp(computed_key, server_key, key_length) == 0;
+	return timingsafe_bcmp(computed_key, server_key, key_length) == 0;
 }
 
 
@@ -1130,9 +1130,9 @@ verify_final_nonce(scram_state *state)
 
 	if (final_nonce_len != client_nonce_len + server_nonce_len)
 		return false;
-	if (memcmp(state->client_final_nonce, state->client_nonce, client_nonce_len) != 0)
+	if (timingsafe_bcmp(state->client_final_nonce, state->client_nonce, client_nonce_len) != 0)
 		return false;
-	if (memcmp(state->client_final_nonce + client_nonce_len, state->server_nonce, server_nonce_len) != 0)
+	if (timingsafe_bcmp(state->client_final_nonce + client_nonce_len, state->server_nonce, server_nonce_len) != 0)
 		return false;
 
 	return true;
@@ -1186,7 +1186,7 @@ verify_client_proof(scram_state *state)
 				client_StoredKey, &errstr) < 0)
 		elog(ERROR, "could not hash stored key: %s", errstr);
 
-	if (memcmp(client_StoredKey, state->StoredKey, state->key_length) != 0)
+	if (timingsafe_bcmp(client_StoredKey, state->StoredKey, state->key_length) != 0)
 		return false;
 
 	return true;
diff --git a/src/backend/libpq/crypt.c b/src/backend/libpq/crypt.c
index 37ccec355c7..739a2e6fa8b 100644
--- a/src/backend/libpq/crypt.c
+++ b/src/backend/libpq/crypt.c
@@ -293,7 +293,8 @@ md5_crypt_verify(const char *role, const char *shadow_pass,
 		return STATUS_ERROR;
 	}
 
-	if (strcmp(client_pass, crypt_pwd) == 0)
+	if (strlen(client_pass) == strlen(crypt_pwd) &&
+		timingsafe_bcmp(client_pass, crypt_pwd, strlen(crypt_pwd)) == 0)
 	{
 		retval = STATUS_OK;
 
@@ -372,7 +373,8 @@ plain_crypt_verify(const char *role, const char *shadow_pass,
 				*logdetail = errstr;
 				return STATUS_ERROR;
 			}
-			if (strcmp(crypt_client_pass, shadow_pass) == 0)
+			if (strlen(crypt_client_pass) == strlen(shadow_pass) &&
+				timingsafe_bcmp(crypt_client_pass, shadow_pass, strlen(shadow_pass)) == 0)
 				return STATUS_OK;
 			else
 			{
diff --git a/src/interfaces/libpq/fe-auth-scram.c b/src/interfaces/libpq/fe-auth-scram.c
index 99103b7e2b6..08c7c666946 100644
--- a/src/interfaces/libpq/fe-auth-scram.c
+++ b/src/interfaces/libpq/fe-auth-scram.c
@@ -631,7 +631,7 @@ read_server_first_message(fe_scram_state *state, char *input)
 
 	/* Verify immediately that the server used our part of the nonce */
 	if (strlen(nonce) < strlen(state->client_nonce) ||
-		memcmp(nonce, state->client_nonce, strlen(state->client_nonce)) != 0)
+		timingsafe_bcmp(nonce, state->client_nonce, strlen(state->client_nonce)) != 0)
 	{
 		libpq_append_conn_error(conn, "invalid SCRAM response (nonce mismatch)");
 		return false;
@@ -896,8 +896,8 @@ verify_server_signature(fe_scram_state *state, bool *match,
 	pg_hmac_free(ctx);
 
 	/* signature processed, so now check after it */
-	if (memcmp(expected_ServerSignature, state->ServerSignature,
-			   state->key_length) != 0)
+	if (timingsafe_bcmp(expected_ServerSignature, state->ServerSignature,
+						state->key_length) != 0)
 		*match = false;
 	else
 		*match = true;